Circuit breakers are used to protect equipment from overcurrent situations caused, for example, by short circuits or ground faults in or near such equipment. In the event an overcurrent condition occurs, electrical contacts within the circuit breaker will open, stopping the flow of electrical current through the circuit breaker to the equipment.
Circuit breakers may include an electronic trip unit that senses electrical current to the protected equipment. If the sensed electrical current indicates an overcurrent situation, the electronic trip unit provides a trip signal to a trip actuator (e.g., a solenoid). In response to the trip signal, the trip actuator actuates (trips) a mechanical operating mechanism. Actuation of the mechanical operating mechanism by the trip actuator causes the mechanical operating mechanism to separate (i.e., open) the electrical contacts, stopping the flow of current to the protected equipment.
In addition to sensing current to the protected equipment, the electronic trip unit may also sense the voltage across the protected equipment. The sensed current and voltage can be used for the purpose of metering quantities including voltage, current, power, energy, and power factor. The traditional method of sensing voltage is to employ potential transformers and a voltage divider to reduce the system voltage to a low level for input to the electronics. Because of space constraints in the circuit breakers, these components are typically mounted external to the circuit breaker housing. Wiring is then run from the output of the voltage divider networks to each circuit breaker. Where a large number of circuit breakers are installed, the wiring needed to accommodate the externally-mounted voltage sensing equipment consumes spaces and increases installation cost.